1. Field of the Invention
The present invention is related to a file control system which is configured by a plurality of file control devices connected to each other and the file control device used in the system, and more specifically, a technique for highly reliable file control preventing data inconsistency when an uncorrectable error occurs during data transfer between the file control devices in the file control system.
2. Description of the Related Art
In order to carry out a smooth and high-speed data transfer between a host computer and an external storage device, a file control device, controlling writing and reading of the data to the external storage device following the command of the host computer, is configured between the host computer and a high-capacity external storage device. The file control device has memory internal, and access time gap between the external storage device and the host computer is eliminated by caching a part of the data in the memory every time the host computer carries out the process. In addition, a file control system etc. with higher reliability has been devised by configuring a plurality of file control devices between the host computer and the external storage device.
The file control device and the file control system stop operations of elements thereof, when an operation error occurs during writing/reading the data in/from the external storage device, and when memory inconsistency occurs, the inconsistency is to be recovered. By so doing, data consistency is maintained (Patent Document 1, for example).
Patent Document 1 discloses a control device (controller), which is able to stop operations of its elements as soon as possible when operation error such as data number error and verification error occurs in an error correcting circuit or DMA controller etc. in the control device controlling an information-recording disk device connected between a host computer and the information-recording disk device.    Patent Document 1: Japanese unexamined patent publication bulletin No. 03-172920 “Controller for Information Recording Disk Device”
The existing control device described in Patent Document 1 transmits signals in the order of an operation abnormality signal, operation error occurrence signal and an operation stop signal as soon as possible, when operation error, such as data number error, verification error and uncorrectable error, occurs in its own elements, and let each element stop its operation. Thus, it is possible to cancel the operation in relatively early timing.
However, in a configuration in which a plurality of file control devices are connected and a plurality of file control devices carry out data transfer (writing/reading) using memory, which each file control device comprises, when an uncorrectable error occurs during data reading of the file control device of the data transmitting side, there is no means for notifying an error to the file control-device of the data receiving side. That is, there is no such item as an error occurrence flag, which indicates whether or not errors occurred in the data, in the items of the redundancy comprised in data. Therefore, the only way to handle the situation is to stop operations of the transmitting side device.
Especially, when the error detection code (CRC, ECC, Parity etc.) used for transferring the data between file control devices and the error detection code reading the data from a memory in a file control device are different, even though the inconsistency between the read data and the error detection code is detected on reading the data from the memory, a new error detection code is generated for the read data (error data) in transferring the data between devices, and the new error code replaces the previous error detection code. Therefore the inconsistency detected by the previous error detection code cannot be detected by the file control device of the receiving side.
Furthermore, if the error data is stored in a memory of the file control device of the data receiving side, by not detecting the inconsistency of the error data included in the data received by the file control device of the receiving side, then, the data may be garbled in the memory of the receiving file control device. Here, a problem is that when control information or address data is garbled in one device, the data failure of the device could affect the performance of the other devices.